Note: Descriptions are shown in the official language in which they were submitted.
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_ ANTI-TWO BLOCK WIRE INTERNAL TO
CRANE TELESCOPIC BOOM
Field of the InVC',lll:lOn
~I~11C 111VC11t1011 1'CIatCS Lo 11T117I"OVC111e11tS 111 Wll'111~"
arranl;cmcnls for
anti-two block devices for cranes.
Background of the Invention
During operation of a crane, if the hook block contacts the boom
nose with enough force, the lifting cable could break and the hook block,
along with the load, would fall to the ground. Such contact of the hook
block and boom nose is called two-blocking, and is a particularly
dangerous situation. Therefore, anti-two block devices are used as an
operator aid on cranes to warn the crane operator that the hook block is
approaching the boom nose. In some systems, in addition to providing a
warning to the operator, control signals will be generated to lock out the
hoist-up function or the telescope-out function for the boom so as to
prevent further operation of the crane that would brim, t~lie hook block
any closer to the boom nose.
Typically, an anti-two block device comprises a weight suspended
by a chain from an electrical switch mounted on or near the boom nose
of a crane. The weight fits around one of the falls of the lifting cable
running from the hook block to the boom nose sheaves. The weight keeps
the electrical contacts of the switch closed, and the crane operator can
freely raise or lower the hook block and/or telescope the boom
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outwardly. If the hook block comes too close to the boom nose, the
weight will be raised and the switch will open. Opening of the switch will
generate a warning to the operator and, as noted above, may cut off any
operation of the crane which would create further likelihood of two-
blocking.
Figures 1-2 illustrate a typical anti-two blocking arrangement on
an extensible crane boom. Figure 2 is an enlarged view of the boom nose
portion of the boom illustrated in Figure 1.
As seen in Figure 1, a typical extensible boom 10 may have, for
example, a base section 12, a mid section 14, and a fly section 16,
although the number of boom sections can vary from that illustrated. A
boom nose portion 18 includes sheaves (not shown) for guiding the lifting
cable 20. Lifting cable 20 supports a hook block (not shown) for lifting a
load.
An anti-two block device might typically include a switch 22
mounted on boom nose portion 18, as best seen in Figur~,2. A weight 24
surrounds cable 20. Weight 24 is suspended by a chairi~'or other linkage
26, and normally holds the electrical contacts closed in switch 22.
Switch 22 is provided with electrical power and is connected to a
control panel in an operator's cab via, for example, a socket 28
associated with switch 22 and a plug 30 associated with an electrical
wire 32. As seen in Figure 1, wire 32 extends along the exterior of boom
10. Wire 32 is guided by a number of cable guides 34 associated with
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base section 12 and additional guides 36, 38 associated with the mid
section and fly sections, respectively. Wire 32 may be used to carry
power to switch 22 an/or to carry signals from switch 22 to the control
cab of the crane.
A reel mechanism 40 is provided on the exterior of the base
section. Reel 40 pays out and takes up wire 32 as the boom extends and
retracts, respectively. As a result, wire 32 is maintained taut at all times
during operation of the boom.
As discussed above, the contacts in switch 22 are normally
maintained closed by weight 24. If the hook block closely approaches the
boom nose 18, the hook block will lift weight 24, whereby the contacts
within switch 22 will be permitted to open. As a result, appropriate
control signals will be generated and transmitted to the control cab
and/or the control panel of the crane via wire 32. A visual and/or
audible warning of the situation may be provided to the operator, and
certain functions of the crane may be disabled to prevent;~,the operator
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from causing the hook block to more closely approach the boom nose.
Such a structure, as described with respect to Figures 1-2, has a
number of drawbacks associated with it. The fact that reel 40 and wire
32 are mounted externally to the boom exposes the reel 40 and wire 32
to many external hazards. For example, wire 32 and/or reel 40 may
sometimes be damaged by becoming snagged on tree limbs, either while
in transport or during operation of the boom around trees. Wire 32
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and/or reel 40 can also become snagged on other job-related objects or
structures.
Exposure to the elements, ice, freezing rain, sleet and snow, can
also cause problems with the wire or the reel. Being exposed to all of
these hazards will sometimes result in wire 32 or reel 40 sustaining
enough damage that the anti-two block device will no longer function
properly.
Additionally, use of reel 40 requires that some mechanism be
provided to maintain electrical continuity between the wire 32 on reel 40
and another conductor element that extends from reel 40 to the control
panel of the crane as the reel rotates. This, together with reel 40, adds
expense and complexity to the elements required to connect the anti-two
block switch to the control panel, possibly also adversely affecting
reliability.
Obiects of the Invention
v, ;
Accordingly, it is an object of tree present invention to overcome the
above-described drawbacks and limitations.
A particular object of the present invention is to overcome these
drawbacks and limitations by providing a structure wherein the wire for
providing power and electrical signals to and from an anti-two block
device is positioned internally of an extensible boom where it is protected
from the above-discussed hazards and elements.
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Another object of the invention is to provide an anti-two block
wiring arrangement that is simple and less prone to mechanical
difficulties and failure.
Summary of the Invention
In accordance with the invention, a signal/power wire for an anti-
two block device is positioned internally of the sections of an extensible
boom. The wire length stays constant, eliminating any need for reels or
other wire take-up devices.
In accordance with the invention, the wire power or signal wire is
routed over pulleys and guide elements located strategically in the
different boom sections to allow the boom to extend and retract while not
requiring a variable length anti-two block wire.
Brief Description of the Drawings
The present invention will be better understood upon consideration
of the following detailed description considered in conjur~~tion with the
. ,,;
accompanying drawings, in which:
Figure 1 illustrates a typical extensible boom that includes an anti-
two block device;
Figure 2 is an enlarged view of the nose portion of the boom of
Figure 1;
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Figure 3 is a side sectional view illustrating a first embodiment of
an extensible boom in accordance with the invention in an extended
condition;
Figure 4 is a side sectional view illustrating the boom of Figure 3 in
a retracted condition;
Figure 5 is an enlargement of certain wire guiding elements of the
embodiment of Figures 3-4 of the present invention;
Figure 6 is a side sectional view illustrating a boom in accordance
with a second embodiment of the present invention in a retracted
condition;
Figure 7 is a side sectional view of the boom of Figure 6 in an
extended condition;
Figure 8 is a view of one section of a boom in accordance with the
embodiment of Figures 6-7 illustrating details of the cable control
arrangement; and
Figure 9 is a partial end view of the embodiment of;~igures 6-8
taken in the direction of arrow 9 of Figure 8.
Detailed Description of Preferred Embodiments
Figures 3-5 illustrate a first embodiment of the invention suitable
for an extensible crane comprising an odd number of sections, such as
three sections. Elements of the boom unnecessary to an understanding
of the invention are omitted for clarity of illustration. In this exemplary
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embodiment, an extensible boom 50 includes a base section 52, a mid
section 54, and a fly section 56. A boom nose 58 is positioned at the
distal end of the fly section. A lifting cable (not shown) passes over
sheaves (also not shown) in boom nose 58 in the normal fashion.
A typical boom extension mechanism includes a piston and
cylinder device. In the example illustrated, an extension rod 60 is
connected to base section 52, and an extension cylinder 62 is connected
to the mid section 54 of the boom. Rod 60 is connected to a piston
internal to cylinder 62, as is well known.
As best seen in Figure 5, extension cable sheaves 64 are mounted
on the end of extension cylinder 62 via supports 66 and an extension
sheave pin 68. Typically, a pair of extension cable sheaves 64 are
provided. In Figure 5 only one sheave 64 is shown for clarity of
illustration. Boom extension cables (not shown) are anchored to base
section 52. The extension cables extend through the interior of the boom,
over and about extension sheaves 64, and are then connected to the
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portion of the fly section 56 that is furthest from the boom nose 58.
To extend the boom, hydraulic~fluid is provided under pressure to
piston-cylinder device 60, 62, thus extending cylinder 62. As cylinder 62
extends, mid section 54 connected to cylinder 62 also telescopes
outwardly with respect to the base section. Outward movement of
extension sheaves 64 together with cylinder 62 causes fly section 56 to
also telescope with respect to mid section 54 via the boom extension
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cables. The boom sections 54 and 56, thus, telescope synchronously and
proportionately to extend the overall length of the boom. Retraction of the
boom, of course, occurs in the opposite manner as a result of retraction
of piston-cylinder device 60, 62 together with the extension cable pulleys
64 and the associated extension cables.
An anti-two block switch is provided at or near boom nose 58, to
be connected to a wire 70 as indicated in Figure 3. The anti-two block
switch can take any form now known or later developed. The particular
form of the anti-two block switch does not itself form part of the present
invention.
According to the present invention, power and control signals pass
between the anti-two block switch and a control panel in the control cab
of the crane via the wire or cable 70. This wire or cable is located entirely
within the interior of boom 50 throughout the length of the boom. Wire
70 is of constant length, and is substantially inextensible. Never the less,
wire 70 is mounted in a manner to accommodate extension and
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retraction of the boom.
A first end 72 of wire 70 is anchored to base section 52. A
connector, shown schematically at 73, can be provided to connect wire
70 to a further conductor that extends from the boom to connect to the
control panel of the crane. Alternately, wire 70 can be extended past its
anchor point at the base section 52 of the boom to itself extend from the
boom to the control panel.
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Wire 70 extends from its anchor point through the boom interior
and passes over and around a wire pulley 74. In the embodiment
illustrated, wire pulley 74 is carried on extension shcave pin 68 between
extension cable sheaves 64. From pulley 74, wire 70 extends to, and is
secured within a wire turnaround clamp 76 mounted on the interior of
fly section 56. Wire 70 then extends through fly section 56 to boom nose
58 where it can be connected to an anti-two block switch.
As boom 50 extends and retracts, wire 70 follows a path similar to
the boom extension cables. Wire 70 provides a power- and signal path
between an anti-two block switch located at boom nose 58 and the base
of the boom so that connection can be made to a control panel in a
control cab of the crane.
The length of wire 70 remains constant and the wire stays taut
throughout extension and retraction of boom 50. A spring mount 78 may
be provided adjacent one end of wire 70. Spring mount 78 keeps wire 70
taut despite small changes in boom length as a result of,,~for example,
,t. ,.
compression of hydraulic fluid within piston-cylinder device 60, 62.
A second embodiment of the present invention will be described
with respect to Figures 6-9. This embodiment is suitable for extensible
booms having an even number of sections. The illustrated example
comprises two sections. This embodiment is suitable for use between
any two adjacent sections of an extensible boom, regardless of the total
number of sections comprising the boom.
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As illustrated in Figures 6-7, an extensible boom 80 is considered
to comprise a base section 82 and a second section 84. In the drawing
figure, section 82 is a base section such as would be mounted on a
support structure of a crane. It is possible, as noted above, that section
82 is itself telescopic with respect to another lower section of the crane.'
Second section 84 is telescopic, with respect to base 82. As
illustrated, section 84 is a fly section comprising a boom nose 58. As
discussed above with respect to Figure 3, boom nose 58 may comprise
sheaves for carrying a lifting cable. It is to be understood, however, as
noted above, that section 84 need not be a fly section. Rather, it may
comprise any section that is telescopic with respect to an adjacent
section.
Boom 80 comprises a device, not illustrated, to extend and retract
section 84 with respect to section 82. This device may take any suitable
form, such as a piston and cylinder device having portions connected to
the sections, respectively, or any suitable equivalent.
,,;
A control wire or cable portion 86 is associated with base section
82. Another control wire or cable portion 86' is associated with second
section 84. These control cable portions may be connected to a control
panel of the apparatus, such as by a connector cable 87, and to an anti-
two block switch at or near boom nose 58.
As best illustrated in Figure 8, control cable portion 86 is anchored
at an anchor point 88 adjacent the lower end of base section 82. Anchor
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88 may include a spring, illustrated schematically at 90. Control cable
86, like wire or cable 70 in the above-described embodiment, is
inextensible, and the cable control mechanism to be described
hereinafter does not provide for changes in length of cable 86. Spring 90
may be provided, however, to keep cable 86 taut despite minor variations
due to, for example, temperature changes, compression of hydraulic fluid
or minor mechanical adjustments of the cable control mechanism.
Control cable 86 passes about a first sheave or pulley 92
associated with a traveling block 94. Cable 86 then passes about a guide
pulley 96 mounted on base section 82. The other end of control cable 86
is secured in an anchor block 98. Anchor block 98 is mounted on second
boom section 84 and is movable therewith. In the embodiment
illustrated, the end-most portion of control cable 86 passes through a
portion of second section 84 to be connected with control cable portion
86'. For convenience, a connector 99 may be provided for this purpose.
When joined together, control cable portions 86, 86' constitute
,.
essentially a continuous, inextensible control cable passing through the
interior of the extensible boom.
The boom in accordance with this second embodiment further
comprises tensioning cable 100. A first end of cable 100 is anchored to
base section 82 at an anchor point 102. Tension cable 100 passes about
a second sheave or pulley 104 associated with traveling block 94, and
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then about another guide pulley 106 mounted on base section 82. The
other end of tension cable 100 is secured to anchor block 98.
The function of tension cable 100, together with traveling block 94,
is to provide an equal and opposite tension force on traveling block 94 to
balance the tension applied by control cable 86. As a result of this
arrangement, the position of control cable portion 86, and the
termination point of control cable 86~ at anchor 98 and connector 99, can
vary to accommodate extension and retraction of the telescopic boom in a
manner to be described in greater detail hereinafter.
As seen in Figure 8 and more particularly in Figure 9, traveling
block 94 is movable linearly with respect to base section 82 along a track
108. Track 108 may be formed as a channel, as is seen in sectional view
in Figure 9, or in any other suitable form. In the exemplary embodiment
illustrated, rollers 110 are associated with sheaves 92 and 104. Such
rollers cooperate with track 108 to facilitate movement of traveling block
94 in either direction along the track. In operation, blocl~,;94 travels along
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track 108 to permit control cable portion 86 to follow the extension or
retraction of telescopic boom section 84.
When the boom is in a retracted condition, as illustrated in Figure
6, anchor 98 associated with the lower end of telescopic section 84 is
positioned generally near the lower end of base section 82. The end of
tensioning cable 100 secured to anchor 98 is also drawn to the lower end
of base section 82. As a result, traveling block 94 is caused to travel
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along tr ack 108 toward the opposite, outer (upper) end of base section
82. This also can be seen in Figure 6. In this configuration, the length of
section 86a of cable portion 86 (see Figure 8) is maximized and the
length of portion 86b is minimized.
Whcn boom section 84 is extended with respect to base section 82,
anchor 98 travels with telescopic section 82 and moves away from the
lower end of base section 82. This pulls control cable: portion 86 outward
in the direction of arrow E (Figure 8). This increases the length of cable
portion 86b to accommodate movement of the second boom section 84.
To accommodate this movement, traveling block 94 travels along track
108 toward the lower end of base section 82, as illustrated in Figure 7.
As is evident from consideration of Figure 8, simultaneously, movement
of anchor 98 toward the upper or outer end of base section 82 permits
portion 100a of tensioning cable 100 to lengthen, thereby permitting
traveling block 94 to travel to the lower end of base section 82.
In accordance with this second embodiment of the;~,present
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invention, a control cable can pass entirely through the interior of a two
section extensible boom, achieving all of the advantages discussed above
with respect to the embodiment of Figures 3-5. The embodiment of
Figures 6-9 is not limited to the specific arrangement illustrated. For
example, traveling block 94, cable portion 86, tension cable 100 and
other associated elements can be associated with the second, telescopic
section 84 while anchor 98 and cable portion 86' can be mounted on
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base section 82. All that would be required to achieve this would be to
reverse the position of all elements.
Additionally, while the embodiment of Figures 6-9 has been
described as including a track such as shown at 108, that element is
optional. In an apparatus constructed in the manner illustrated, with
the arrangement of the anchor points 98 and 102 and the guide pulleys
96 and 106, the tension in cable portion 86 and cable 100 causes the
travelling block 94 to travel in a straight line from one end of its traverse
to the other without further guidance or control, such as from a track,
being necessary.
It is also possible to combine the embodiments of Figures 3-5 and
6-9, respectively, in order to provide a control cable passing through the
interior of an extensible boom having any number of sections. For
example, the second embodiment of Figures 6-9 could be combined with
the embodiment of Figures 3-5 to accommodate a boom having four
sections. A plurality of control cable arrangements in accordance with
the embodiment of Figures 6-9 could be included in a$~ociation with a
series of adjacent telescopic boom sections of a single boom having
virtually any number of sections. Virtually any combination of the above
embodiments may be adapted to accommodate specific needs and booms
having particular numbers of telescopic sections.
The wire or cable arrangement according to the present invention
satisfies all requirements for supply of electrical power to the boom nose
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for an anti-two bloclc switch, or any other device requiring a connection
for signals or power, and for returning control signals to the control cab.
The internal wire is easily replaceable without disassembling the boom.
The anti-two block wire internal to a crane telescopic boom in
accordance with the invention eliminates the drawbacks associated with
a typical electrical reel and wire mounted externally of a boom. When
employing a wire/cable arrangement according to the invention, there
can be no physical contact between the wire internal to the boom and
external hazards such as tree limbs~and other objects. Also, the wire is
not exposed to the elements as in the previously-known arrangements.
While the present invention has been disclosed and described with
respect to a control wire or cable internal to an extensible crane boom
and an anti-two block switch, it is not so limited. An internal control
cable arrangement in accordance with the invention is suitable, for
example, for connecting controls at the platform on the end of a boom in
an aerial work platform to controlled devices mounted at or near the base
of the boom. An arrangement in accordance with the invention is
suitable to connect any device or control at one end of an extensible
boom to another device or control at the other end of the boom.
is
